Method and apparatus for drilling a curved bore in an object

ABSTRACT

A method and apparatus for drilling a curved bore are disclosed, wherein the apparatus includes a handle (20) and a removable cartridge (174) in which cutting bits (240) are disposed to produce the bore. The handle includes a trigger (66), (66&#39;), or (66&#34;), which the user squeezes toward a grip (24) of the handle to both energize a pneumatic motor (42) and to advance the opposed cutting bits in curved arcs at different rates. As the trigger is squeezed, a curved guide arm (234) conveying one of the cutting bits is advanced more rapidly than the other curved guide arm, passing a median point in the bore and then being withdrawn as the other curved guide arm and cutting bit are advanced past the median point. Thus, interference between the two cutting bits is avoided and a clean bore hole is produced. In addition, the removable cartridge minimizes breakage of a flexible drive cable (238) used to transmit rotational force to the cutting bits from rotating left and right extended drive shafts (190) and 192). A straight segment (236) of each curved guide arm is provided adjacent the point where the cutting bit connects to the flexible drive cable, to substantially eliminate stress on the flexible drive cable at that point. Instead, the stress is shifted to a portion of the flexible shaft where its flexibility is greater. A push-button release (122) is provided on a barrel (26&#39;) of the handle to facilitate release of retainer pins (106&#39;) that engage push bars in the removable cartridge so that the removable cartridge can more easily be disengaged from the barrel.

This is a divisional of the prior application Ser. No. 08/059,834, filedon May 11, 1993, to be issued as U.S. Pat. No. 5, 509,918, on Apr. 23,1996, of Jack W. Romano for APPARATUS FOR DRILLING A CURVED BORE IN ANOBJECT, the benefit of the filing date of which are hereby claimed under35 U.S. C. § 120.

FIELD OF THE INVENTION

This invention generally relates to a method and apparatus for drillinga curved bore in an object, and more specifically, to drilling a curvedbore using two cutting bits that are advanced through intersecting arcsto form the curved bore in the object.

BACKGROUND OF THE INVENTION

There are many applications in which it is desirable to drill a curvedbore in an object. For example, in orthopedic surgery, a number ofprocedures require a surgeon to secure tissue to bone by using stitchesthat extend through holes made in the bone; these procedures wouldbenefit greatly if apparatus were commercially available that wouldallow a curved bore to be efficiently formed in the bone. Instead, theprocedure typically employed requires that two angled bores be drilledin the bone, with the hope that the straight bores will intersect sothat a curved surgical needle can be forced through the bore withoutbreaking or jamming. To accommodate the curvature of the needle, thestraight bores must be larger in diameter than is desired. In addition,there is often limited working space available where the holes must bedrilled, making it difficult to maneuver a drill to produce the twostraight holes from opposed angles. Of course, there are many industrialprocesses that would also benefit if low cost apparatus werecommercially available that could produce smoothly curved bores in anobject. Accordingly, the applications of such apparatus are not in anyway limited to the medical field.

A solution to the problem of producing a curved bore is disclosed in twoearlier U.S. Pat. Nos. 4,941,466 and 5,002,546, issued to the inventorof the present invention. In the first of these patents, a curved boredrilling apparatus and method are disclosed in which two driven shaftsare provided with flexible shaft sections, each having a cutting tip. Asemicircular curved drill guide attached to a pivotally mounted swingarm loosely engages and carries each flexible shaft and cutting tip. Twolinkage rods couple the drill guides to a push rod that advance thecutting tips so that they simultaneously swing toward each other inintersecting 90° arcs. The push rod is advanced by moving a pivotalhandle relative to a stationary handle. In a second embodiment, thedrill guides are simultaneously rotated toward each other by a worm andpinion drive actuated by the operator.

U.S. Pat. No. 5,002,546 discloses several different embodiments ofapparatus for producing a curved bore using various machining processesin addition to the cutting tips. The apparatus disclosed for supportingthe cutting tips and drive mechanism is shaped like a handgun; a triggeris mechanically coupled to various alternative linkages for advancingthe cutting means to form the curved bore.

A significant problem with the apparatus for drilling a curved boredisclosed in these two patents relates to an interference between thetwo cutting tips that occurs when the cutting tips are swung toward eachother to meet at about the center of the curved bore. Clearly, it isdesirable that the bore be smoothly completed at its center or medianpoint; yet, advancing both cutting tips simultaneously to meet at thecenter of the bore, as disclosed in this prior an, can cause the twocutting tips to be damaged as their cutting faces rotate against eachother and can leave a rough circumferential lip at the median point,because neither cutting tip passes that point. One solution to thisproblem not disclosed in the prior an patents is to separately advancethe cutting tips so that first one crosses over the median point in thebore and is then backed up before the other is advanced past the medianpoint. In this manner, the two cutting tips never contact each other,but both rotate with their curved guide past the median point tocomplete a smooth curved bore in the object. Since the prior an does notdisclose or suggest this technique, it clearly also fails to discloseany mechanism suitable for accomplishing the task.

Using two levers to independently advance the opposed cutting tipsthrough their respective arcs at different times would achieve thedesired goal, but is neither a very elegant nor a particularly practicalsolution to the problem. Ideally, the apparatus for drilling a curvedbore should be capable of operation using only one hand, withoutrequiring the user to manipulate separate control levers to advance eachcutting tip. Manipulating separate levers to advance the two cuttingtips at different times would likely require both hands and would be anunduly complex and difficult operation to repetitively complete, whenproducing multiple curved bores.

Another issue that is not disclosed in the prior art is the problem andsolution for dealing with wear of the flexible drive cables and dullingof the cutting tips that will inevitably occur from time to time. Arelated issue concerns the need for producing different size anddifferent radius bores without requiring that a different integral drivedevice be provided for producing each size and radius bore. The designof the apparatus for producing curved bores disclosed in the above-notedreferences does not readily facilitate replacement of the flexible drivecable and cutting tips, nor does it disclose a mechanism for changingthe cutting tips and curved guides as appropriate to produce differentsize or different radius bores, while continuing to use the samerotational drive and advancement mechanism. Provision for couplingdifferent radii curved guides or different diameter cutting bits housedin removable cartridges with a common drive mechanism offers acost-efficient solution to this problem.

Because the radius of curvature defined by the path of the bore producedby the apparatus can be relatively small, e.g., less than 0.5 in., theflexible cable driving the cutting bit is forced through acorrespondingly small radius of curvature. The point of attachment ofthe cutting tip or bit to the flexible cable is an area of substantiallyreduced flexibility in the cable, and unfortunately, is also a point ofgreat stress. It has been observed that any breakage of the flexiblecable during use of the curved bore drilling apparatus is more likely tooccur adjacent the cutting tip than elsewhere. Accordingly, it is clearthat some modification of the prior art apparatus is desirable to extendthe useful life of the flexible cable.

SUMMARY OF THE INVENTION

In accordance with the present invention, apparatus for drilling acurved bore in an object include a prime mover for providing arotational drive force and a pair of flexible cables, each having aproximal end and a distal end. The proximal end is coupled to the primemover so as to rotate in response to the rotational drive force itprovides, and the distal end is coupled to a cutting bit. A housing isprovided that also has a distal end and a proximal end, the distal endbeing positioned adjacent the object in order to drill the curved bore.The flexible cables extend at least part way through the housing. A pairof curved guides are pivotally mounted to rotate in intersectingcoplanar arcs and each curved guide supports the distal end of one ofthe flexible cables. As the pair of curved guides are pivotally rotatedoutwardly toward each other from the distal end of the housing, theydefine a path followed by each of the cutting bits as they are rotatedto cut the curved bore in an object. The cutting bits are thus supportedby the curved guides and rotated by the flexible cables. A pair oflevers are pivotally mounted to the housing at pivot pins, and eachlever is mechanically coupled to a different one of the curved guides torotate the curved guide through the coplanar am when the lever ispivoted about its pivot pin. The levers advance the cutting bits along acommon portion of the path at different times to produce the curved borein the object, so that the cutting bits do not contact each other.

In a first preferred form of the invention, one of the levers comprisesa trigger, and means moved by the trigger are provided for pivotallyrotating the other lever in first one direction and then in an oppositedirection as the trigger is pivoted in only one direction, so that thecutting bits are moved as follows. First, one of the cutting bits iscarried past an intermediate point in the path of the bore by the curvedguide coupled to the other lever. Next, that cutting bit is thenwithdrawn from the intermediate point in the path of the bore. Finally,the other cutting bit is carried past the intermediate point to completethe bore, thus avoiding contact between the cutting bits.

The apparatus further includes a control for actuating the prime mover,and the trigger activates the control as the trigger is pivotally movedfrom a rest position to apply the driving force to advance the cuttingbit in order to produce the curved bore hole.

Alternatively, another preferred form of the invention includes aseparate trigger, and a linkage mechanically coupling the trigger toboth levers. Movement of the trigger in only one direction causes one ofthe levers to pivotally move in a first direction and then in a seconddirection that is opposite the first direction, while the other levermoves only in a first direction. The one lever thereby initiallyadvances one of the cutting bits to pivot past an intermediate point inthe path of the curved bore, and then to retract along that path as theother cutting bit advances past the intermediate point from the oppositeend of the path to complete the curved bore. In one form of thisembodiment, the linkage comprises a pair of cams rotatably driven bymovement of the trigger. The cams have different surfaces of rotation.Each lever follows the surface of rotation of a different one of thepair of cams, and the shape of a cam determines the movement of thelever tracking along its surface of rotation, so that the movement isdifferent for each lever.

Another form of the immediately preceding embodiment includes linkagethat comprise a ramped surface moved by the trigger, which the leverscontact at different points. Each lever contacts and moves along adifferent part of the ramped surface so that movement of the triggercauses the levers to move differently.

Means for adjusting an extent by which pivotal movement of the leversmoves the curved guides and the cutting bits are preferably provided toproduce curved bore holes of different radii using curved guides ofcorrespondingly different radii. The means for adjusting include a pairof links. Each link extends between one of the curved guides and one ofthe levers and has an angled portion adjacent the lever that is formedat an angle selected to contact the lever at a defined distance from thepivot pin of the lever. This distance determines a range of pivotalmotion of a selected curved guide having a specific radius of curvature.

The housing preferably comprises a handle portion and a removablecartridge portion through which the flexible cables extend. The pair ofcurved guides are disposed and pivotally mounted in the removablecartridge portion. Disconnectable drive couplings are included tomechanically couple the prime mover to the flexible cables, anddisconnectable links mechanically couple the levers to the curvedguides. Thus, the removable cartridge and flexible cables can readily beattached and disconnected from the handle and disconnectable drivecouplings, respectively. The cartridge portion is sized to engage thehandle portion. The disconnectable links each comprise two sections thatreleasably couple together. Means are provided for unlatching the twosections of the disconnectable links when the cartridge portion isremoved from the handle portion of the housing. The disconnectable linkseach comprise a spring-biased pin on one section of the disconnectablelink. Preferably, the means for unlatching comprise a release pin on thehandle portion that acts on the spring-biased pin to open the latch forremoving the cartridge portion from the handle portion.

Another aspect of the present invention is a method for drilling acurved bore in an object. This method comprises steps that are generallyconsistent with the functions provided by each of the elements of theapparatus discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIGS. 1A, 1B, and 1C are side views of a handle for a first embodimentof the present invention, with one side of a housing of the handleremoved in all three views, and the lower portion of the handle cut-awayin the latter two views to better disclose the components containedtherein, the three views respectively showing a trigger in threesuccessive positions to illustrate the different movement of the twocutter guide push rods in response to rotation of the trigger;

FIGS. 2A, 2B, and 2C are top plan views of the handle, with the top ofthe chamber and barrel cut away to more clearly disclose therelationship of the two cutter guide push rods, with respect tocorresponding FIGS. 1A, 1B, and 1C;

FIG. 3A is a side view of part of a handle for a second embodiment ofthe invention, with one side of a housing of the handle removed tobetter disclose the components contained therein;

FIG. 3B is a front cutaway view of a portion of the handle of FIG. 3Awherein an internal drive gear is disclosed that accommodates differentspacing between drive shafts to facilitate use of the handle to drivecutting bits in removable cartridges designed to produce bore holes ofsubstantially different radii of curvature;

FIG. 4A is a side view of part of a handle for a third embodiment of theinvention, with one side of a advancement the handle removed to betterdisclose the cam advancement components contained therein;

FIG. 4B is a simplified front cutaway view of a portion of the handleshown in FIG. 4A, illustrating the cam advancement mechanism foradvancing the cutter guide via movement of push rods;

FIG. 5 is an isometric view of a portion of the barrel and of aremovable cartridge that engages the barrel to couple with the driveshafts and push rods used to provide rotational driving motion and tocontrol the advancement of the cutting bits, respectively;

FIGS. 6A and 6B are simplified side views of an end of the barrel, withthe side of the barrel partially cut away and a proximal end of thecartridge removed to more deafly show a preferred embodiment forreleasable dips (only one shown) that couple push rods in the barrelwith push bars in the cartridge;

FIG. 6C shows a plan view of an alternative embodiment for a releasemechanism adapted to be fitted to the barrel (shown in phantom view) toactuate the releasable clips;

FIG. 6D is a side elevational view of the release mechanism of FIG. 6C,showing how it is mounted on the barrel (a portion of which is shown inphantom view);

FIG. 7 is a plan view of one of the two opposed curved cutter guides anda flexible cable having a cutting bit attached to one end;

FIG. 8 is an exploded isometric view of the removable cartridge showingthe flexible drive cables and other elements of the invention disposedtherein; and

FIGS. 9A, 9B, and 9C are three plan views of the removable cartridge,with the distal portion of the top housing cut away to reveal thedifferential advancement of the two opposed cutting bits from a restposition (FIG. 9A), at a point where one of the cutting bits is fullyadvanced past a median point in the bore (FIG. 9B), and then, at a pointwhere the other cutting bit is fully advanced past the median point tocomplete the bore (FIG. 9C).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The apparatus for drilling a curved bore in accordance with the presentinvention includes a removable cartridge 174 (shown in FIGS. 5, 8, and9A through 9C), which is used in conjunction with a hand-held drillingenergy carrier or drive mechanism. In a first embodiment of thishand-held drive mechanism shown in FIGS. 1A, 1B, and 1C, a handle 20 isillustrated with a left side of a housing 22 removed to disclose thecomponents of the drive mechanism that provide a rotational force torotate cutting bits 240 (FIG. 8) and also control the advancement of thecutting bits to produce the curved bore--when coupled to removablecartridge 174. Details of the removable cartridge and of the mechanismfor pivoting the cutting bits through intersecting arcs to produce thecurved bore are disclosed below, following a disclosure of the variousembodiments of the handle.

Description of Three Embodiments for the Handle

Referring first to FIG. 1A, handle 20 comprises housing 22, of whichonly the right side is shown. Housing 22 is shaped like a pistol,including a grip 24, a barrel 26, and a chamber 28 in which most of therotational drive and cutting bit advancement mechanism is disposed. Itwill be apparent that the left side of housing 22 has been removed ineach of FIGS. 1A, 1B, and 1C to more clearly show the components of thismechanism. At the bottom of grip 24 is disposed an inlet port 30, whichis adapted to couple to a pneumatic air line fitting (not shown) thatsupplies pressurized air to handle 20 through a flexible air lineconnected to an air compressor (neither shown). Inlet port 30 has afitting 32 that is connected through a line to the inlet of an air valve34, which is normally closed to interrupt air flow to the outlet of theair valve. At the top of air valve 34 is disposed a valve stem 36,having a general dome shape configuration, which facilitates depressionof the valve stem to open air valve 34. When valve stem 36 is depressedinto the body of air valve 34, pressurized air flows from the inlet,through the air valve, and from the outlet through a line 38 into amotor inlet port 40. To better illustrate the disposition of line 38,the line between fitting 32 and the inlet of air valve 34 has beenremoved in these figures. The pressurized air energizes a pneumaticmotor 42, causing a drive shaft 48 to rotate. It will be understood thatan electric motor, hydraulic motor, or other type of prime mover couldalternatively be employed to rotate drive shaft 48. Drive shaft 48extends upwardly from the top of pneumatic motor 42 and is coupled torotate a bevel gear 46.

A mounting bracket 50a supports pneumatic motor 42 and air valve 34within grip 24. In addition, in chamber 28, mounting bracket 50asupports a bearing 52a in which one end of an idler shaft 54 turns. Theopposite end of idler shaft 54 is supported by a bearing 52b within amounting bracket 50b that is attached to housing 22.

Bevel gear 46 engages a bevel gear 56 that is coupled to idler shaft 54,causing the idler shaft to rotate when pneumatic motor 42 is energizedwith pressurized air. Air at a relatively lower pressure and highervolume than that applied to motor inlet port 40 exits pneumatic motor 42through a muffler outlet port 44, which is disposed at the base of grip24. Although not shown, a conventional pneumatic muffler is readilyconnected to muffler outlet port 44 to substantially silence the flow ofexhaust air from pneumatic motor 42.

As idler shaft 54 rotates, a drive gear 58 that is connected to theidler shaft between bearings 52a and 52b also rotates. Drive gear 58meshes with a left driven gear 60 and with a right driven gear 118 (asmore clearly shown in FIGS. 2A, 2B, and 2C). Mounting bracket 50b alsosupports a left drive shaft 62 to which left driven gear 60 is attached.Left drive shaft 62 extends through barrel 26, and a left drive coupling64 is connected to left drive shaft 62 adjacent the distal end of thebarrel. Similarly, a right drive shaft 120 is supported by mountingbracket 50b and is rotated by right driven gear 118. Right drive shaft120 extends through the barrel and is connected to a right drivecoupling 122 adjacent the distal end of barrel 26. Both left drive shaft62 and right drive shaft 120 are supported by a bearing block 124 atabout the midpoint position along the length of the barrel.

A trigger 66 is mounted to housing 22 at a pivot pin 68 so that as thetrigger is squeezed by the fingers of a user toward grip 24, the triggerrotates about pivot pin 68, moving an upwardly extending lever portion70 of trigger 66 in a short arc. Lever portion 70 engages a link 72b,which is attached to a right push rod 102. In addition, as trigger 66 issqueezed toward grip 24, a lever 74 disposed behind the trigger isrotated about a pivot pin 76. The lower end of lever 74 includes aroller 78, which rides on a cam block 80. Cam block 80 is attached tothe back side of trigger 66 and includes two surfaces over which roller78 rides, including an "advance" surface 82 and a "fall-off" surface 84,the significance of which will shortly be evident. The upper end oflever 74 engages a link 72a, which is connected to a left push rod 100(only a small portion of which is shown in FIGS. 1A-1C). Left push rod100 also extends through barrel 26, toward its distal end, generallyparallel to right push rod 102. Bearing block 124 is relieved along itstop surface to provide clearance and support for the left and right pushrods, which extend beyond the bearing block.

To provide a biasing force that tends to resist rotation of lever 74when trigger 66 is squeezed toward grip 24, a helical coiled spring 86is looped around a from edge of lever 74, extending between a bolt 88and a bolt 90 that secure the ends of the spring to mounting bracket50b. A biasing force that resists squeezing and pivotal movement oftrigger 66 is provided by a helical coil spring 94, which extends fromthe rear of a valve actuator slide 92 to the front surface of air valve34. Valve actuator slide 92 has a zigzag shape, extending from a tip 96on its lower portion to a tip 98, which abuts against valve stem 36. Astrigger 66 is initially squeezed toward grip 24, the rear surface of thetrigger contacts tip 96, valve actuator slide 92 compresses helicalcoiled spring 94, and tip 98 depresses valve stem 36, enablingpressurized air flow through air valve 34.

At substantially the same time that movement of trigger 66 opens airvalve 34 to energize pneumatic motor 42, the ramped slope defined byadvance surface 82 on cam block 80 acts on roller 78, causing lever 74to rotate about pivot pin 76 and advancing link 72b and left push rod100 to which it is connected from their normal rest positions, to moreforward positions, i.e., moving left push rod 100 toward the distal endof barrel 26. As trigger 66 is initially squeezed toward grip 24, lever74 rotates about pivot pin 76 to move left push rod 100 sooner and to agreater extent than upwardly extending lever portion 70 rotating aboutpivot pin 68 initially moves right push rod 102. Thus, left push rod 100advances more rapidly than right push rod 102.

Referring now to FIG. 1B and corresponding FIG 2B, the relationshipbetween the left and right push rods 100 and 102 due to rotation ofupwardly extending lever portion 70 and lever 74 is clearly illustrated.At the intermediate point in the rotation of trigger 66 represented ifFIGURE 1B, roller 78 on the lower end of lever 74 is disposed at thevery end of advance surface 82 on cam block 80. Left push rod 100 hasadvanced a left clip 104 that is attached to the left push rod adjacentan opening 114 at the distal end of barrel 26 to about a maximumdisplacement (shown in FIG. 2A) relative to its original rest position.As will become apparent during the discussion of the removable cartridgethat is coupled to barrel 26 and as shown in FIGS. 9A through 9C, thedisplacement of left clip 104 shown in FIG. 2B corresponds to pivotingof cutting bit 240, which is disposed on the right in the removablecartridge, past a median point in a curved bore 254 being formed in anobject 252. To complete the curved bore, it is necessary for the opposedcutting bit on the left to subsequently also be advanced past the medianpoint, thereby creating a clean curved bore without any circumferentiallip at the medium, as would result if both the cutting bits weresimultaneously advanced to meet at the median point in the bore.

To avoid interference between the linkage and damage to the two cuttingbits 240 that would occur if they contacted each other, left clip 104must be retracted from its maximum displaced position shown in FIG. 2Bbefore right clip 116 is advanced to a point of maximum displacement, asshown in FIG. 2C. FIG. 2C corresponds to the fully rotated position oftrigger 66 shown in FIG. 1C. It will be noted in FIG. 1C that roller 78on the lower portion of lever 74 has moved from advance surface 82,dropping onto fall-off surface 84, thereby allowing lever 74 to move ina retrograde direction relative to its initial movement that occurredwhen trigger 66 was initially squeezed toward grip 24. As a result ofthe retrograde motion of lever 74, left clip 104, as shown deafly inFIG. 2C, has moved behind the point of maximum displacement of rightclip 116. Since left clip 104 and right clip 116 are advanced atdifferent rates and do not reach a maximum forward displacementsimultaneously, interference between the cutting bits in a removablecartridge to which they are coupled is avoided.

A second embodiment of a handle 20' is shown in FIG. 3A. Any of thecomponents of the present invention associated with handle 20' that areidentical in function and form to those discussed above in regard tohandle 20 have the same reference numerals. However, those elementsassociated with handle 20' that have the same function but differentform or configuration from those of handle 20 include a primedesignation in their reference number. Thus for example, a housing 22',which is different in shape than housing 22, is used in connection withhandle 20'; a chamber 28' has a slightly larger volume than chamber 28to accommodate a bevel internal gear 56'.

Bevel internal gear 56' is mounted and supported to freely turn within abearing 52', which in turn, is supported by a mounting bracket 50a'.Bevel internal gear 56' meshes with and is driven by bevel gear 46.

As shown in FIG. 3B, a left driven gear 60' is attached to the end of aleft drive shaft 62' (although appearing on the right in the view ofFIG. 3B) and is drivingly rotated by bevel internal gear 56'. Similarly,a right drive shaft 120', having a right driven gear 118 mounted on itsend is also drivingly rotated by bevel internal gear 56'. One of theadvantages of bevel internal gear 56' over bevel internal gear 56 in thefirst embodiment, is its ability to apply rotational force to left andright drive shafts that are spaced apart in varying degree, and thereby,to accommodate removable cartridges configured to produce curved boreholes of significantly different radii. For example, as shown in phantomview, left and right gears 146 and 148 am mounted to engage bevelinternal gear 56' at a substantially wider spacing (exaggerated) thanleft and right driven gears 60' and 118'. Although a limited variationin the radii of the curved bore made with different cartridges (e.g.,+0.2 in.) can be accommodated without changing the spacing between theleft and right drive shafts, more significant changes in radii requirewider bodied removable cartridges that are designed to couple with morewidely spaced left and right drive shafts. Small variations in thevertical position of left and right drive shafts 62' and 120' thatoccurs when the spacing between them is changed are readily accommodatedwithin the space allocated inside barrel 26 of handle 20'.

Referring to FIG. 3A, it will be apparent that a different advancementmechanism is used to control the advancement of a left push rod 100' anda similar right push rod (not shown). Specifically, in this embodiment,a trigger 66' is mounted to pivotally rotate about a pivot pin 68'.However, unlike trigger 66, which was used in handle 20 (shown in FIG.1A through FIG. 1C), trigger 66' does not directly advance one of thepush rods. Instead, a left lever 134 and a corresponding right lever 142are provided to couple the rotational motion of trigger 66 into theadvancement of the left and right push rods. Only the lower portion ofright lever 142 is shown in FIG. 3A, since it is hidden behind leftlever 134 over most of its length; however, although shorter at itslower end below pivot pin 138, right lever 142 is otherwisesubstantially identical to left lever 134. The lower end of right lever142 includes a roller 144. Similarly, the lower end of left lever 134includes a roller 140 that rides along cam block 80 ahead of roller 144.As a result, left lever 134 advances left push rod 100' to its maximumdisplaced position before right lever 142 advances the other push rod tothat extent. Thereafter, roller 140 drops onto fill-off surface 84 oncam block 80, allowing left push rod 100 to move in a retrograde motionrelative to its initial advancement. However, roller 144 continues toroll along the advance surface of cam block 80 until the other push rodto which it is coupled has reached its maximum forward displacement. Itshould be noted that separate cam blocks can alternatively be attachedto the back of trigger 66' for rollers 140 and 142, independentlycontrolling the rate at which the left and right levers pivotallyrotate.

A helical coil spring 86' provides a biasing force that resists theforward rotation of the upper portion of left and right levers 134 and142. Simultaneously with the rotational movement of trigger 66' toinitially advance push rod 100', valve actuator slide 92 depresses valvestem 36, opening air valve 34. Thus, in handle 20', squeezing trigger66' has substantially the same net effect in terms of advancing firstone cutting bit and then the other past a median point in the circularbore while pressurized air is applied to energize pneumatic motor 42 andthus to provide rotational force to rotate the cutting bits.

To further accommodate removable cartridges designed to produce bores ofsubstantially different radii, the left and right push rods are coupledto separate adjustable links 130 (only one visible in FIG. 3A), whichcan be positioned at different points along the length of left and rightlevers 134 and 142. The surface of these two levers that contacts theend of adjustable link 130 includes a series of notches 136 toaccommodate positioning the adjustable link so that the same relativeangular movement of left and right levers 134 and 142 results in adifferent displacement of the two push rods. For example, adjustablelink 130 is shown in a position 132 in phantom view that would produce asubstantially greater displacement of the left push rod for a givenrotation of the trigger 66'. The greater advancement of the push rodsfor a given angular displacement of the levers thus achieved may berequired for a removable cartridge designed to produce a circular borehaving a substantially greater radius compared to that which would beproduced by the removable cartridge coupled to handle 20', withadjustable link 130 placed in the (non-phantom) position shown in FIG.3A. Inclusion of adjustable link 130 thus enables handle 20' to beconfigured for advancing the cutting bits in removable cartridges byvarying degrees, to produce curved bores of substantially differentradii, thereby eliminating the need to provide completely differentconfiguration handles for each removable cartridge designed to producebore holes of different radii of curvature.

A third embodiment for the handle is shown generally at referencenumeral 20" in FIG. 4A. FIG. 4B shows a cutaway view of handle 20",viewed from just behind a trigger 66". Again, reference numerals thatare common to the first embodiment shown in FIGS. 1 A-1C are used foridentical elements, and primes are added to reference numerals ofelements having common functions but different configurations. Forexample, trigger 66" pivots about a pivot pin 68', but does not includea cam block 80 as did the triggers in the first two embodiments.Instead, the rear surface of trigger 66" contacts a tip 96' on a valveactuator slide 92' as the trigger is squeezed toward grip 24. Movementof valve actuator slide 92' again causes tip 98 to depress valve stem36, opening air valve 34 to provide pressurized air to energizepneumatic motor 42. At the same time, valve actuator slide 92' rotates apinion gear 152, which meshes with a gear rack 150 formed on the uppersurface of valve actuator slide 92'.

As shown more dearly in FIG. 4B, pinion gear 152 is attached to a shaft154 that extends between opposite sides of housing 22 and is rotatablydriven by the gear. A left cam 156 is disposed on the left side of valveactuator slide 92 and a right cam 158 on the other side. Rotation ofpinion gear 152 occurring when a user squeezes trigger 66" rotates leftand right cams 156 and 158 in a counterclockwise direction, as shown inFIG. 4A.

Left cam 156 preferably has a different shape than right cam 158 toensure that left push rod 100 is advanced to its maximum displacementbefore right push rod 102, and then moves in an opposite direction.Alternatively, the left and right cams can have the same shape, but bemounted at different rotational positions on shaft 154. A left lever 160rides along the surface of rotation of left cam 156 as it rotates sothat the relative change in radius of the left cam produces acorresponding rotation of left lever 160 about a pivot pin 138'.

Similarly, a right lever 162 rides on the surface of rotation of rightcam 158 as it rotates, advancing link 72b and its connected right pushrod 102 to a point of maximum displacement after push rod 100 has beguna retrograde motion to pull back from its point of maximum displacement.Helical springs 164 apply a bias force that resists rotation of left andright levers 160 and 162 to advance link 72a and 72b, respectively. Onceagain, the differential movement of the left and right push rods avoidsinterference between opposed cutting bits in the removable cartridge asthe bits are swung in an are to form the curved bore.

Description of the Removable Cartridge and Its Engagement with Handle

FIG. 5 illustrates a portion of barrel 26 and removable cartridge 174that is positioned to engage the barrel. The removable cartridgecomprises a housing 176 that comprises a top 176a and a bottom 176b,held together with threaded fasteners 148 that mate with threaded holes150 in bottom 176b. Alternatively, the top and bottom of housing 176 canbe adhesively or ultrasonically bonded together. Housing 176 has aproximal end 178, a flared shoulder 198 that is adjacent the proximalend, and a distal end 180, within which are disposed the opposed cuttingbits. The opening of distal end 180 of the removable cartridge defines aconcave curve suitable for placement against a rounded object into whichthe curved bore is to be formed. Proximal end 178 is sized and shaped tofit within opening 114 at the distal end of barrel 26.

Inside opening 114 at the distal end of barrel 26, left drive coupling64 includes a relieved opening 170 having an internal regular hexagonalconfiguration to mate with a corresponding left hexagonal fitting 186that extends from the distal end of the removable cartridge. Similarly,a right hexagonal fitting 188 mates with right drive coupling 122, whichis disposed at the end of right drive shaft 120. Relieved openings 170in both the left and right drive couplings and a rounded tip on left andright hexagonal fittings 186 and 188 ensures that the hexagonal fittingsreadily slide into the relieved openings and engage the drive couplings.The left and right hexagonal fittings are connected to extended left andright drive shafts 190 and 192 that run in substantially parallelalignment through the length of the removable cartridge. Helical coilsprings 194 that are concentric around the left and right extended driveshafts at proximal end 178 provide a biasing force tending to maintainthe left and right hexagonal fittings in a rearwardly extendingposition, i.e., extending outwardly from proximal end 178 of removablecartridge 174. Flared shoulder 198 is intended to abut against thedistal end of barrel 26 as proximal end 178 is slidably engaged withinopening 114 of the barrel.

Between the left and right extended drive shafts 190 and 192 in theremovable cartridge are disposed left and right push bars 182 and 184,respectively. Left and right push bars 182 and 184 are adapted to coupleto corresponding left and right clips 104 and 116, which are disposed inbarrel 26 at the distal ends of left push rods 100 and right push rod102, respectively. Specifically, left and right push bars 182 and 184slide into slots 172 formed within the left and right clips and areengaged by retainer pins 106. Grooves 112, formed internally, on thesides of barrel 26 also engage ridges 196 formed along each side ofproximal end 178 of removable cartridge 174, in a friction fit. It willbe apparent that the disposition of the grooves and ridges can beinterchanged, so that the grooves are formed on the sides of theproximal end of removable cartridge 174 and the ridges are formedinternally on the sides of barrel 26. When the proximal end of removablecartridge 174 is inserted within opening 114 on barrel 26, therotational drive force conveyed through both the left and right driveshafts are coupled via the left and right drive couplings to theextended left and right drive shafts through the hexagonal fittings. Theforce used to advance the cutting bits is coupled from left and rightpush rods 100 and 102 into left and right push bars 182 and 184 as thepush bars engage left and right clips 104 and 116. As the left and rightpush bars move, the hexagonal fitting slides longitudinally inside thedrive couplings.

Details of a preferred embodiment for left and right clips 104 and 116are shown in FIGS. 6A and 6B. In addition, an alternative embodiment ofa barrel 26' is illustrated that includes a release button 222, whichfacilitates releasing a retainer pin 106' from an aperture 210 formed inleft push bar 182. A corresponding aperture 210 is formed in right pushbar 184, which is not visible in FIGS. 6A and 6B. Release button 222 isgenerally Π-shaped and is mounted on barrel 26' and biased outwardly bya pair of helical coil springs 224 (only one of which is shown) that areconcentric with the two depending stems of the release button. The lowerends of these stems on release button 222 are flattened to ensure theirretention inside barrel 26'.

In FIG. 6A, details of left clip 104 (partially cut away) are shown.Left clip 104 includes a rivet 110 that extends vertically through theclip to attach flexures 108 to the top and bottom of the clip. A pivotpin 220 extends between opposed sides of the clip, pivotally supportingretainer pin 106'. Flexures 108 provide a bias force that tends to keepretainer pin 106' in the position shown in FIG. 6A, so that a tang 212on the retainer pin engages aperture 210 when the removable cartridge isengaged in the end of barrel 26'. To facilitate removal of thecartridge, release button 222 is depressed by the user as shown by thearrow in FIG. 6B. When thus depressed, the lower end of one of the stemson release button 222 forces a lever arm 214 of the retainer pin topivot downwardly about pivot pin 220, against the biasing forcedeveloped by deflection of flexures 108. This rotational movement of theretainer pin causes tangs 212 to withdraw from apertures 210, easing thedisengagement of the removable cartridge from barrel 26'. Alternatively,with respect to barrel 26, tangs 212 on retainer pins 106 have a roundeddome shape and the apertures that they engage on the ends of the leftand right push bars can be formed as open slots, facilitatingdisengagement of push bars 182 and 184 from left and right clips 104 and116, respectively, simply by pulling the removable cartridge to extractit from barrel 26 with sufficient force to overcome the biasing force offlexures 108.

FIGS. 6C and 6D illustrate an alternative to release button 222 in whicha flexure release lever 216 stamped from sheet metal has two downwardlydepending tabs 218 at one end that are sized to act on lever arms 214 ofretainer pins 106' when the upwardly extending end of the flexurerelease lever is depressed by the user. When thus depressed, downwardlydepending tabs 218 cause retainer pins 106' pivot so that tangs 212 arewithdrawn from apertures 210. The removable cartridge can then bereadily withdrawn from a barrel 26" (shown in phantom view) to which theflexure release lever is fastened with threaded fasteners 217. Springbias force in the flexure release lever restores it to the positionwhere it suspended above the top of barrel 26". Flexure release lever216 is a lower cost, simpler design than release button 222, but equallyeffective in accomplishing the task of releasing the left and right pushbars of the removable cartridge from the left and right push rods in thebarrel.

Description of the Components Inside the Removable Cartridge

Details of an exemplary swing arm 230 and curved guide arm 234 are shownin FIG. 7. Identical swing arms 230 and guide arms 234 are provided forboth of the opposed cutting bits 240, but the guide arm for one of thecutting bits is inverted when mounted at distal end 180 of the removablecartridge. Swing arm 230 includes one of the two pivot pins 200, whichis used to pivotally mount the swing arm at the distal end of removablecartridge 174. A constant radius of curvature R defines the distancebetween the center of pivot pin 200 and the exterior surface of thecurved guide arm, along the inside circumference of its curvature aboutpivot pin 200. However, the radius between the center of pivot pin 200and the internal circumferential surface of the curved guide arm againstwhich the flexible drive cable is guided, is not constant. Instead, theinner wall thickness of the curved guide arm varies of the length of itscurve, causing the radius between the internal surface and the center ofpivot pin 200 to vary accordingly, as explained below. The cutting bitsproduce a curved bore 254 having a radius of curvature that is slightlydifferent than (R+D/2), where D is the diameter of the cutting bit,because of the separation between the centers of the two pivot pins 200and because the pivot pins are necessarily set back from the insidecurve at the distal end of the removable cartridge.

Each cutting bit 240 is soldered or otherwise fastened to a flexibledrive cable 238 that conveys a rotational drive force to the cutting bitfrom one of the left or right extended drive shafts 190 or 192 to whichthe other end of the flexible drive cable is attached. As each curvedguide arm 234 is pivoted outwardly from distal end 180 in a coplanar arcwith the other curved guide arm, the cutting bit produces a curved borehaving a diameter D that is greater than the diameter of curved guidearm 234 with flexible drive cable 238 in place. The flexible drive cableis constrained on the inside of its curved path by curved guide arm 234and on the outside of the curved path by the bore that the cutting bitis producing. The larger diameter of cutting bit 240 provides theclearance required for flexible drive cable 238 and curved guide arm 234to advance freely through the bore behind the cutting bit. Cutting bit240 is loosely supported and carried with curved guide arm 234 duringits pivotal rotation about one of pivot pins 200, so that the flexibledrive cable wraps around the curved guide arm through the are of itstravel. This are intersects the are formed by the other curved guide armand the partial bore that the other cutting bit produces to complete thecurved bore since the two arcs are coplanar. However, each curved guideann is swung outward beyond a median point within the bore hole at adifferent time by the mechanism in handles 20, 20' or 20", so that theopposed cutting bits do not contact each other.

As noted above in the Background of the Invention, one of the problemsrecognized with the prior art design for producing a curved bore holeusing two opposed cutting bits is the problem of breakage incurred inthe flexible drive cable, particularly at the point where the cuttingbit attaches to the flexible drive cable. Since left drive shaft 62,right drive shaft 120, and left and right extended shafts 190 and 192are solid, they have considerably greater resistance to breakage thandoes flexible drive cable 238, which comprises a plurality of wirestrands and is generally of very small diameter, e.g., less than 0.05in. In particular, it has been determined that the flexible drive 238cable has a substantially reduced flexibility in the vicinity wherecutting bit 240 is attached to the flexible drive cable, i.e., justbehind the cutting bit; therefore, it is important to avoid flexure offlexible drive cables 238 in this region. Accordingly, curved guide arm234 is curved along substantially its entire length, except at the endadjacent cutting bit 240, where it includes a relatively short,substantially straight segment 236. The distal end of straight segment236 extends around the shank of cutting bit 240 and serves as a thrustbearing for the cutting bit. To provide the straight segment, the wallthickness of curved guide arm 234 along the inner circumference isslightly relieved or tapered along its curved length. It is thistapering of the wall thickness that causes the variation in the radiusbetween pivot pin 200 and the inside surface of the curved guide arm.For example, this radius is equal to r₁ at the bearing portion ofstraight segment 236, changes to r₂ behind the bearing portion, and isequal to r₃ at the beginning of the straight segment, where r₁, r₂, andr₃ are all unequal radii. Straight segment 236 thus avoids flexure offlexible drive cable 238 where it attaches to the cutting bit, since theflexible drive cable is least able to handle the stress at this point,and shifts the flexure to a portion of the flexible drive cable proximalof the straight segment, where the flexible drive cable can betterwithstand the stress, thereby reducing the likelihood of flexible drivecable breakage. It will be apparent that an alternative curved guide arm(not shown) having constant thickness wall, e.g., a metal stamped part,could also be used, if formed to provide a substantially straightsegment adjacent the cutting bit.

Preferably, housing 176 of removable cartridge 174 is formed of alow-cost injection molded plastic. Since it is virtually impossible toeconomically sterilize removable cartridge 174 after use in a surgicalprocedure to produce one or more curved bores in the bone of a patientundergoing the surgical procedure, it is important that removablecartridge 174 be of low cost and designed to be discarded after use witha single patient. For this reason, it is important that the removablecartridge be made of inexpensive materials and easily engaged withhandle 20, 20", or 20", so that the removable cartridge can be readilyreplaced. These criteria are also likely to be important in industrialapplications.

FIG. 8 and FIGS. 9A through 9C disclose further details of removablecartridge 174. For example, in FIG. 8, an exploded view illustrates abottom housing 176b through which left and right extended drive shafts188 and 190 convey rotational force from the proximal to distal ends ofthe removable cartridge. The ends of the left and right extended shaftsare coupled to flexible drive cables 238, which convey the rotationalforce to cutting bits 240. Left push bar 182 is coupled to a push link244 to convey the force to advance cutting bit 240 by pivoting one ofswing arms 230 and the curved guide arm that supports the cutting bit inan am about pivot pin 200. Similarly, right push bar 184 is coupled toanother push link 244, which conveys the force to advance the otherswing arm 230 and the other curved guide arm that supports the othercutting bit 240 in an arc to form the other part of the bore in anobject. Each push link 244 is formed with an offset between the part ofthe push link that pivots about a pivot pin 242 at swing arm 230 and thepart that pivots about a pivot pin 246 at the left or right push bar 182or 184. The offset in push links 244 provide clearance relative to swingarms 230 as the two swing arms are pivoted outwardly about pivot pins200 to produce the curved bore with the cutting bits.

Turning now to FIGS. 9A, 9B, and 9C, the relative positions of the twoopposed cutting bits 240 are illustrated as they would appear atsuccessive times during the formation of curved bore 254 in an object252. The cutting bits are shown in a rest position in FIG. 9A, before auser begins squeezing the trigger against the grip on the handle. InFIG. 9B, the trigger has moved part way through its complete range oftravel, causing left push bar 182 to advance from its rest position.Displacement of the left push bar is transmitted through push link 244,which is connected between that push bar and swing arm 230, so thatcutting bit 240 is pivoted outwardly by the curved guide arm to cut apartial curved bore that extends past a median point in the completedcurved bore to be formed in object 252. (The median point is indicatedby the dash line.) The object is abutted against distal end 180 ofremovable cartridge 174. Further movement of the trigger producesretrograde displacement of left push bar 182, causing the cutting bit240 on the right, which is supported by the swing arm coupled to theleft push bar, to withdraw back away from the median point in the boreas right push bar 184 continues to advance the other swing arm 230 andcurved guide arm on the left. Further advancement of push bar 184advances the other cutting bit past the median point to complete curvedbore 254 in object 252. When the trigger is released, both cutting bits240 return to their normal rest position as shown in FIG. 9A.Accordingly, the present invention produces curved bore 254 withinobject 252 without risk of cutting bits 240 contacting each other, andthe curved bore is substantially smoother than would be the case ifneither cutting bit had passed the median point.

While the present invention has been disclosed with respect to severalpreferred embodiments, those of ordinary skill in the art willappreciate that further changes to the invention can be made within thescope of the claims that follow. Accordingly, it is not intended thatthe scope of the invention be in any way limited by the disclosure ofthe preferred embodiments set forth above, but instead that it bedetermined entirely by reference to the claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. Apparatus for drilling acurved bore in a object, comprising:(a) a housing having a distal endand a proximal end, the distal end being adapted to position adjacent anobject to be drilled, the proximal end being adapted to couple with adrive housing; (b) opposed first and second cutting bits, each coupledto a corresponding first and second flexible cable, said first andsecond cutting bits being disposed adjacent the distal end of thehousing and rotated by the first and second flexible cables, said firstand second flexible cables extending through the housing and terminatingin disconnectable drive couplings adjacent the proximal end of saidhousing, rotation of the drive couplings by an externally appliedrotational force being transmitted through the first and second flexiblecables to rotatably drive the first and second cutting bits; (c) a firstand a second curved guide supporting the corresponding first and secondflexible cables and corresponding first and second cutting bits, saidfirst and second curved guides being pivotally mounted adjacent thedistal end of the housing and swingable about a pivot in opposed,intersecting coplanar arcs along a path that defines the bore in theobject; and (d) first and second links having proximal and distal ends,the first and second links being mounted in the housing for movementindependently of each other such that one link can be moved withoutequal and corresponding movement of the other link, the distal ends ofsaid first and second links being coupled mechanically to thecorresponding first and second curved guides, independently of thecoupling of the first and second flexible cables to the first and secondcutting bits, for controlling swinging of the first and second curvedguides about the pivot, the proximal ends of said first and second linksbeing attachable to disconnectable fittings, so that an external forceapplied to the first and second links is transmitted through the firstand second links to swing the first and second curved guides and thefirst and second cutting bits outwardly from the distal end of thehousing to produce the curved bore.
 2. The apparatus of claim 1, whereinthe housing comprises a cartridge that is adapted to couple with a drivehandle that provides the external rotational drive force to rotate thefirst and second flexible cables and the externally applied force toswing the first and second curved guides.
 3. The apparatus of claim 2,wherein the cartridge includes means for detachably engaging the drivehandle, to enable the cartridge to be readily attached and removed fromthe drive handle.
 4. The apparatus of claim 1, wherein the first andsecond curved guides each include a substantially straight segmentadjacent the first and second cutting bits, respectively, said straightsegment minimizing flexure of the first and second flexible cables wheresaid first and second cables are attached to the first and secondcutting bits, reduce stress and consequential breakage of the first andsecond flexible cables.
 5. The apparatus of claim 4, wherein an innerwall thickness of the first and second curved guides is relieved inthickness to produce the straight segments.
 6. The apparatus of claim 1,wherein the first and second links are adapted to slidably engage with alatch that applies the externally applied force.
 7. The apparatus ofclaim 1, wherein the disconnectable drive couplings on the first andsecond flexible cables slidably engage corresponding mating fittingsthat rotate to provide the externally applied rotational force.
 8. Adrive handle in combination with and adapted to be coupled to theapparatus defined in claim 1, and having disconnectble couplings adaptedto mate with the disconnectable couplings of the first and secondflexible cables and disconnectable fittings adapted to mate with theproximal ends of the first and second links, for connection of the drivehandle to and separation of the drive handle from the housing, and fortransfer of force through the mated couplings and the mated fittings torotate the cutting bits and to swing the curved guides.
 9. The drivehandle defined in claim 8, in which the disconnectable couplings of thehandle slidably engage the disconnectable couplings of the flexiblecables.
 10. Apparatus for drilling a curved bore, comprising:(a) a primemover for providing drilling energy; (b) a pair of flexible drillingenergy transfer members each having a proximal end that is operablycoupled to the prime mover and a distal end operably coupled to acutting member; (c) a housing through which the transfer members extend,said housing having a distal end; (d) a pair of curved guides that arepivotally mounted to swing relative to the housing in arcs thatintersect at a location fixed relative to the housing, each curved guidesupporting the distal end of one of the transfer members, so that assaid pair of curved guides are swung outwardly toward each other fromthe distal end of the housing, they define a continuous composite pathdefined by the cutting members as they are swung relative to the housingto bore the curved bore, said cutting members being supported by thecurved guides and the transfer members; (e) a pair of levers, each leverbeing pivotally mounted to the housing at a pivot pin and mechanicallycoupled to a different one of the curved guides to swing that curvedguide through the coplanar are when the lever is pivoted about its pivotpin; and (f) means for controlling movement of said levers so as toadvance the cutting members along a common portion of the path atdifferent times, to produce the curved bore without the cutting memberscontacting each other.
 11. The apparatus defined in claim 10, in whichthe movement controlling means includes a trigger mechanically coupledto the levers, the trigger also being coupled to the prime mover foractuating the prime mover to supply drilling energy in coordination withmovement of the levers.
 12. Apparatus for drilling a curved bore in anobject, comprising:(a) a cartridge having a distal end and a proximalend, the distal end being adapted to be positioned adjacent to an objectto be drilled, the proximal end being adapted to be detachably coupledwith a handle; (b) opposed first and second cutting members, eachcoupled to a corresponding first and second flexible drilling energytransfer member, said first and second cutting members being disposedadjacent to the distal end of the cartridge for receiving drillingenergy by way of the first and second transfer members, said first andsecond transfer members extending through the cartridge and terminatingin respective first and second disconnectable couplings adjacent to theproximal end of the cartridge, drilling energy by an externally appliedsource being transmittable through the couplings and the first andsecond transfer members to the first and second cutting members; (c) afirst curved guide and a second curved guide supporting thecorresponding first and second transfer members and corresponding firstand second cutting members, said first and second curved guides beingpivotally mounted adjacent to the distal end of the cartridge forswinging in opposed, intersecting arcs along a path that defines thecurved bore in the object; and (d) first and second pusher bars coupledto the first and second curved guides, independently of the coupling ofthe first and second transfer members to the first and second cuttingmembers, for controlling outward movement of the first and second curvedguides to produce the curved bore by the associated first and secondcutting members, the pusher bars being supported in the cartridge formovement independently of each other such that one curved guide can beadvanced without equal and corresponding advancement of the other curvedguide, the pusher bars having proximate ends adapted to couple to anduncouple from the handle, so that an external force by a motion-inducingmechanism in the handle induces motion of the pusher bars to controlmovement of the curved guides.
 13. A drive handle adapted to be coupledto the apparatus defined in claim 12, and having disconnectablecouplings adapted to mate with the disconnectable couplings of thecartridge for connection of the drive handle to and separation of thedrive handle from the cartridge and for transfer of drilling energythrough the mated couplings.
 14. The drive handle defined in claim 13,in which the disconnectable couplings of the handle slidably engage thedisconnectable couplings of the cartridge.
 15. The drive handle definedin claim 14, in which the disconnectable couplings of the handleinterengage the disconnectable couplings of the cartridge fortransferring eternally applied rotational force therethrough.
 16. Thedrive handle defined in claim 13, including disconnectable fittings forcoupling to and uncoupling from the proximal ends of the pusher bars andfor transfer of force through such fittings to induce motion of thepusher bars to control movement of the curved guides.
 17. Apparatus fordrilling a curved bore, comprising an elongated flexible member fortransferring drilling energy, said flexible member having a proximal endand a distal end, a cutting member coupled to the distal end of theflexible member, and a curved guide for receiving a distal end portionof the flexible member, said curved guide having a first segmentadjacent to the cutting member for maintaining a predetermined angularrelationship between the cutting member and the immediately adjacentdistal end of the flexible member and a second curved segment locatedproximally of the first segment, the second curved segment being curvedlengthwise to a greater degree than the curvature of the first segment,such that the first segment is curved less sharply adjacent to thecutting member than the second segment is curved at a locationproximally of the first segment.
 18. The apparatus defined in claim 17,in which the curved guide is movable with the flexable member duringcutting of a bore.
 19. The apparatus defined in claim 18, in which theflexible member is mounted for translation toward and away from thedrill guide as the drill guide is moved.
 20. The apparatus defined inclaim 19, in which the curved guide is of channel cross section forminga groove for reception of the flexible member.
 21. The apparatus definedin claim 17, in which the first segment of the curved guide issubstantially linear for maintaining a linear relationship between thecutting member and the flexible member in the area of coupling of thecutting member to the flexible member.
 22. The apparatus defined inclaim 17, in which the curved guide has a smooth transition between thefirst segment and the second segment.
 23. The apparatus defined in claim17, in which the maximum cross sectional size of the cutting member isgreater than the maximum cross sectional size of the curved guide suchthat the bore drilled by the cutting member has a diameter greater thanthe maximum diameter of the curved guide adjacent to the cutting member.24. The apparatus defined in claim 17, in which the curvature of thecurved guide is different at different distances from its distal end.25. A method for drilling curved bores in an object comprising the stepsof:(a) coupling a pair of flexible drilling energy transfer members to asource of drilling energy, each transfer member having a proximal end towhich the source of drilling energy is coupled and a distal end coupledto a cutting member; (b) positioning the cutting members adjacent to theobject and supporting the distal ends of the transfer members and thecutting members in curved guides; (c) swinging the curved guides to movethe cutting members in arcs that intersect; and (d) advancing thecutting members through an intersecting portion of the arcs at differenttimes, to produced the curved bore in the object without the cuttingmembers contacting each other.
 26. A method for drilling a curved borein an object comprising the steps of:(a) attaching a housing cartridgeportion to a handle portion, such cartridge portion having a pair offlexible drilling energy transfer members each having a proximal end forcoupling to a source of drilling energy and a distal end coupled to acutting member; (b) providing drilling energy to the transfer members;(c) positioning the housing cartridge portion adjacent to the object andsupporting the distal ends of the flexible drive transfer members andthe cutting members in curved guides; (d) moving the cutting members inarcs that intersect, including advancing the cutting members through anintersecting portion of such arcs at different times, to produce thecurved bore in the object without the cutting members contacting eachother.
 27. A method for drilling a bore in an object comprising thesteps of:(a) providing drilling energy to two separate cutting members,each of such cutting members being mounted in a common housing formovement relatively toward and away from each other; and (b) moving thecutting members along respective curved paths through the object whichpaths intersect, in coordinated timed fashion such that one of thecutting members moves first to and then in an opposite direction awayfrom a point of intersection of the paths, followed by movement of theother cutting member to the point of intersection to complete the bore,without the cutting members interfering with each other.
 28. A methodfor drilling a bore in an object comprising the steps of:(a) providingdrilling energy to separate cutting members, each of such cuttingmembers being mounted in a common housing for movement relatively towardand away from each other; (b) moving one of the cutting members along acurved path through the object; and (c) moving the other cutting memberalong a path through the object which intersects the curved path, thecutting members being moved along their respective paths in coordinatedtime fashion such that one of the cutting members moves first to andthen in an opposite direction away from a point of intersection of thepaths, followed by movement of the other cutting member to the point ofintersection to complete the bore, without the cutting membersinterfering with each other.
 29. The method of cutting a curved borewhich comprises:(a) transferring drilling energy to a cutting memberalong an elongated flexible drilling energy transfer member coupled tothe cutting member; and (b) moving the cutting member along a curvedpath of predetermined radius of curvature, while maintaining a distalportion of the flexible member adjacent to the cutting member at agreater radius of curvature, to lessen flexure of the flexible member atits location of coupling to the cutting member.
 30. Apparatus fordrilling a curved bore comprising:(a) a drilling energy carrier; (b) acurvilinear shaped drill guide for guiding the drilling energy carrier;(c) a cutting member; (d) means for positioning the cutting member at adistal end of the drill guide; and (e) means for mounting the curvedguide for swinging so as to move the cutting member along a curved pathhaving a first radius of curvature, the curved guide having meansadjacent to the distal end for positioning the drilling energy carrieralong a curvature less sharply curved at a location just adjacent to thecutting member than the curvature of the curved path.
 31. The apparatusdefined in claim 30, in which the drilling energy carrier is mounted fortranslation toward and away from the drill guide as the drill guide isswung.
 32. The apparatus defined in claim 31, in which the curved guideis of channel cross section forming a groove for reception of thedrilling energy carrier.
 33. The apparatus defined in claim 30, in whichthe drilling energy carrier extends substantially linearly at a locationjust adjacent to the cutting member.
 34. The apparatus defined in claim30, in which the maximum cross sectional size of the cutting member isgreater than the maximum cross sectional size of the drill guide suchthat the bore drilled by the cutting member has a diameter greater thanthe maximum diameter of the curved guide adjacent to the cutting member.35. The apparatus defined in claim 30, in which the curvature of thecurved guide is different at different distances from its distal end.